Background and Objectives: Sleep deprivation and coffee caffeine consumption have been shown to affect glucose homeostasis separately, but the combined effects of these two variables are unknown. Methods and Study Design: Forty-two healthy Iranian men, aged 20-40 years old, were assigned to three groups in a randomised crossover trial involving three treatments with two-week washout periods. Subjects were moderate coffee consumers (≤3 cups/day), and had a Pittsburgh Sleep Quality Index ≤5. Each treatment involved three nights of deprived sleep (4 hrs. in bed) plus 3×150 cc/cup of boiled water (BW treatment), decaffeinated coffee (DC treatment, without sugar, 99.9% caffeine-free), and caffeinated coffee (CC treatment, without sugar, 65 mg caffeine/ cup). DC and CC treatments were blinded. At the end of each treatment, fasting serum glucose (using enzyme assays) and insulin (using electrochemiluminescence immunoassay) were measured and, again, two hours after an oral glucose tolerance test (OGTT). Insulin resistance was quantified with the homeostasis model. Results: Repeated measures ANOVA indicated no significant difference between the treatments in fasting serum glucose (p=0.248) or insulin resistance (p=0.079). However, ANOVA demonstrated differences between treatments in fasting serum insulin (p=0.004) and glucose, as well as insulin after OGTT (p＜0.001). Pairwise comparisons test (within subjects) showed that the CC treatment yielded higher serum glucose and insulin after OGTT (p＜0.001), higher fasting serum insulin (p=0.001), and increased insulin resistance (p=0.039) as compared to the DC treatment. Conclusions: Thus caffeinated coffee was more adverse for glucose homeostasis compared to decaffeinated coffee in individuals who were simultaneously sleep deprived.